1. Field of the Invention
The present invention relates to a non-tacky composite resin composition of a polyurethane-polyvinyl chloride series, and a process for the preparation of the composition.
2. Related Background Art
Polyvinyl chloride type resins (hereinafter the term "polyvinyl chloride" is referred to as "PVC") in combination with a low-molecular weight plasticizer such a dioctyl phthalate are used as general-purpose non-rigid PVC resins in variety of application fields. The non-rigid PVC resins, however, have defects of low oil resistance, low heat-resistance, low adhesiveness, etc. caused by extraction, migration, etc. of the low-molecular-weight plasticizer.
To improve the defects, polymer alloys by blending or copolymerization of a polyurethane resin (hereinafter the term "polyurethane" is referred to as "PU") and PVC have been known to give a sufficiently non-rigid PVC-PU type composite resin without using a low-molecular-weight plasticizer which is liable to be extracted or migrate.
However, in producing such a non-rigid PVC-PU type composite resin, a large quantity of soft PU is required. The PVC-PU type composite resin prepared by using a large quantity of PU resin has defects such as strong surface tackiness, etc. For example, the problems are encountered that lumping occurs on storage, and that mold-releasing property is poor on thermoforming such as injection molding, which lowers processability. The surface tackiness frequent)y hinders practical use of the products. In particular, powder sinter molding of a conventional PVC-PU type composite resin does not give products having satisfactory mechanical and surface properties because the PU component is not readily fusible under non-shearing conditions. From these reasons, application fields of the PVC-PU type composite resins are frequently limited in spite of their superior properties. In some application fields, a lubricant such as a higher fatty acid, silicone oil, etc., a dusting powder such as talc, etc. or a filler such as calcium carbonate, etc. is added to improve processability and surface tackiness of the products. However, &he use of the lubricant cause inconveniences of decrease of adhesiveness, or staining of the mold owing to migration of lubricant to the surface upon molding, and the use of a dusting powder or a filler may lower the transparency of the product or may deteriorate stain resistance.
For the purpose of avoiding such inconveniences, a group represented by any of the general formulas (1) to (3): ##STR2## (where Me is methyl, and m is an integer of 1.ltoreq.m.ltoreq.450), is introduced into the polyurethane molecule to prevent the migration of the lubricant to the surface and to improve slipping properties and mold releasing properties of the PU.
However, the PVC-PU type composite resins produced by using a polyurethane having the group represented by the above general formula (I), (2), or (3) are not sufficiently improved in the lumping-prevention effect and mold-releasing property as desired, and yet are impaired considerably in adhesiveness, although the adhesiveness is an important characteristic of the PVC-PU type composite resins.